THE PROFUSION OF DARK SEPTATE ENDOPHYTIC FUNGI IN NON-ECTOMYCORRHIZALFINE ROOTS OF FOREST TREES AND SHRUBS

Endophytic fungi were isolated from surface-sterilized non-ectomycorrh izal fine roots of 14 shrub and forest tree species of the northern te mperate zone. With the exception of three host species, between 70 and 100% of the roots of each host yielded endophytic fungi. Species dive rsity was low. Thirty-five taxa were found, nine of them in more than 1% of the 421 tree/shrub individuals examined. Dark septate endophytes (DSE; Mycelium radicis atrovirens-complex) dominated the fungal assem blages of coniferous and ericaceous hosts. About one fifth of the DSE sporulated after 1 yr of incubation at 4 degrees C and in darkness, an d could be identified as Phialocephala fortinii. P. fortinii could be isolated from a wide range of hosts and sites (Abies alba, Calluna vul garis, Fagus sylvatica, Picea abies, Pinus sylvestris and Vaccinium my rtillus in Switzerland; Alnus rubra and Gaultheria shallon in Canada; Picea abies and Pinus sylvestris in Germany; Pinus sylvestris in Finla nd). Thus, P. fortinii seems to be neither host- nor site-specific. Fo ur morphological types were recognized among the DSE-isolates. Type 1 was distinctly different because its serial mycelium was very sparse o r absent. In contrast to other types, type 1 never sporulated. Thus, t ype 1 isolates probably belong to a separate taxon. Most isolates were of type 2. About one quarter of the type 2, type 3 and type 4 isolate s sporulated and could be identified as P. fortinii. Types 3 and 4 are supposed to be variants of type 2. The relative proportion of each ty pe seemed to depend on the site, but a clear pattern of host or site p reference could not be recognized. Differences between types in microm orphology of colonies grown on water agar overlaid with cellophane she ets were minimal and therefore cannot be used for routine differentiat ion. The features of the DSE observed in root squashes corresponded we ll with those detected in synthesis experiments or pathogenicity tests with P. fortinii in other studies. In this study DSE were never seen in root tissues proximal to the innermost phellogen. Cryptosporiopsis radicicola was isolated most frequently from roots of F. sylvatica but constituted only a minor component of the fungal assemblages of A. al ba, Pic. abies, and Pin. sylvestris.